Cancer imaging is important for tumor detection, determination of prognosis and treatments, image guided surgery and irradiation, as well as for monitoring responses. Molecular imaging of specific targets could identify tumor types and enable selection of appropriate drugs. Although x-ray imaging is widely used and more rapid with higher resolution compared to PET, SPECT, and MRI, there are currently no targeted x-ray contrast agents. In this proposal we will develop molecular targeted agents for mammography by a nanotechnology approach using gold nanoparticles for imaging cancers. The Her 2 protein on breast cancer cells will be targeted by use of antibodies attached to biocompatible gold nanoparticles using a mouse model. This would then be useful for non-invasive in vivo detection of this mutation which occurs in about 30% of human breast cancers that could then be beneficially treated with the monoclonal antibody Herceptin(r). Molecular mammography imaging would improve on the limited sampling afforded by painful biopsies and provide more thorough detection of even small tumors and metastases missed by biopsies and other methods. It would enable earlier detection of breast cancer. Better tumor definition would also improve precise radiotherapy, surgery, and follow-up monitoring. If successful, this technology could be applied to other tumors for early detection and biochemical typing for more effective individualized treatments. To Public Health: A novel method using nanotechnology will be developed for improved non-invasive imaging and detection of breast cancer types by mammography. This should not only enable better early detection of smaller tumors and metastases without painful biopsies, but identify tumor types so that specific drugs for the type can be administered. Such a need exists to detect Her2 breast cancers, which account for about 30% of breast cancers, where the specific drug Herceptin(r) is available and improves survival.